Human hair has a variety of textures, from fine to coarse, and from straight to curly. The ability to alter or change the texture of hair through chemical processes is important both for men and women, and hair care products and chemical processes that can alter the texture of hair are in great demand. For example, individuals with excessively curly hair seek products that can straighten or "relax" hair.
The relaxing process operates by changing the chemical structure of hair fibers. Hair fibers are comprised of keratin, which is in turn comprised of polypeptide chains bonded together by three types of bonds: cystine (or disulfide) bonds, hydrogen bonds and salt linkages. The relaxing process operates primarily on the cystine bonds. When the cystine bonds are exposed to an alkaline relaxing solution, they are transformed to lanthionine bonds. The chemical term for the hair relaxation process is lanthionization.
In a typical relaxation process, an alkaline relaxing cream is applied to the hair for a time period sufficient to obtain the desired degree of relaxation, typically about 18-20 minutes. During this step, hair visually becomes physically straighter. After the alkaline relaxing cream has been left on the hair for the desired time, it is usually rinsed from the hair with water.
Although the conventional relaxation process decreases the amount of curl in hair, it also damages the hair. The conventional relaxation process causes hair fibers to longitudinally split and break, leaving hair coarse, brittle and unmanageable, which is described in U.S. Pat. No. 5,348,737, which is hereby incorporated by reference. These results cannot be corrected by applying conditioning agents to the hair subsequent to the relaxation process. Therefore, individuals wishing to straighten their hair using the conventional relaxation process must suffer the damaging structural effects of the process on their hair.
It is a/so known that hair fibers swell in the presence of water, and that excessive swelling can also result in structural damage to hair fibers. Swelling occurs in both the hair fiber cortex and the hair fiber cuticle, the respective inner and outer portions of the hair fiber. Structural damage to the fiber occurs when the cortex continues to swell after the cuticle has ceased swelling causing the cuticle to rupture, thereby rendering the hair damaged, dull and difficult to manage. Moreover, the damage done to the hair during relaxation can result in a decrease in the tensile strength of the hair which can cause difficulties when combing the hair while it is either wet or dry.
In general, hair relaxers can be purchased in the form of creams which contain active ingredients such as sodium hydroxide (lye) or guanidine hydroxide. (Compositions that contain guanidine hydroxide have been called "No Lye" relaxers.) Both lye containing relaxers and relaxers that do not contain lye, when applied to hair, decrease the tensile strength of hair considerably. For example, the hair fibers can lose as much as 45-55% of their tensile strength when the hair fibers are wet.
The present invention provides a process for relaxing hair fibers in which swelling is minimized and damage to the resulting hair fibers is also significantly decreased. Also provided is a composition for relaxing hair fibers which provides for decreased hair fiber swelling and decreased damage of the hair fibers.